The Spectrum of Isotropic Diffuse Gamma-Ray Emission between 100 MeV and 820 GeV

Collaboration, Fermi Lat; Ackermann, Markus; Ajello, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; de Angelis, A.; Chekhtman, A.; de Palma, F.; Chiang, J.; Chiaro, G.; Ciprini, S.; do Couto e. Silva, E.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cuoco, A.; Cutini, S.; D'Ammando, F.; Dermer, C. D.; Digel, S. W.; Silva, E. do Couto E.; Drell, P. S.; Do, E.; Favuzzi, C.; Ferrara, E. C.; Focke, W. B.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Godfrey, G.; Gomez-Vargas, G. A.; Grenier, I. A.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hayashi, K.; Hays, E.; Hewitt, J. W.; Ippoliti, P.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kamae, T.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Manfreda, A.; Massaro, F.; Mayer, Michael; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nemmen, R.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Romani, R. W.; Sánchez-Conde, M.; Sg, C.; Schaal, M.; Schulz, A.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Strong, A. W.; Suson, D. J.; Takahashi, H.; Thayer, J. G.; Thayer, J. B.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vianello, G.; Werner, M.; Winer, B. L.; Wood, K. S.; Wood, M.; Zaharijas, G.; Zimmer, S.

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American Astronomical Society, Astrophysical Journal, 1(799), p. 86, 2015

DOI: 10.1088/0004-637x/799/1/86

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The Spectrum of Isotropic Diffuse Gamma-Ray Emission between 100 MeV and 820 GeV

Journal article published in 2014 by Fermi Lat Collaboration, Markus Ackermann

, M. Ajello

, A. Albert, W. B. Atwood, L. Baldini

, J. Ballet

, G. Barbiellini, D. Bastieri

, K. Bechtol, R. Bellazzini, E. Bissaldi

, R. D. Blandford, E. D. Bloom, E. Bottacini and other authors.

This paper is made freely available by the publisher.

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Abstract

The {γ}-ray sky can be decomposed into individually detected sources, diffuse emission attributed to the interactions of Galactic cosmic rays with gas and radiation fields, and a residual all-sky emission component commonly called the isotropic diffuse {γ}-ray background (IGRB). The IGRB comprises all extragalactic emissions too faint or too diffuse to be resolved in a given survey, as well as any residual Galactic foregrounds that are approximately isotropic. The first IGRB measurement with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) used 10 months of sky-survey data and considered an energy range between 200 MeV and 100 GeV. Improvements in event selection and characterization of cosmic-ray backgrounds, better understanding of the diffuse Galactic emission, and a longer data accumulation of 50 months, allow for a refinement and extension of the IGRB measurement with the LAT, now covering the energy range from 100 MeV to 820 GeV. The IGRB spectrum shows a significant high-energy cutoff feature, and can be well described over nearly four decades in energy by a power law with exponential cutoff having a spectral index of $2.32±0.02$ and a break energy of $(279±52)$ GeV using our baseline diffuse Galactic emission model. The total intensity attributed to the IGRB is $(7.2±0.6) \times 10^{-6}$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$ above 100 MeV, with an additional $+15$%/$-30$% systematic uncertainty due to the Galactic diffuse foregrounds.

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The Spectrum of Isotropic Diffuse Gamma-Ray Emission between 100 MeV and 820 GeV

Abstract